The invention relates to a method for implementing single-hop terminal-to-terminal connections with the optimal use of the resources in a geosynchronous mobile satellite system. The invention further relates to a system for providing a direct single-hop communication link between two mobile users with the optimal use of satellite resources.
A number of systems exist which provide both mobile terrestrial communication (i.e., cellular communication) and mobile satellite communication between terminals. Such a system is hereinafter referred to as an MSAT system. Satellite communication between two terminals is typically implemented via a double-hop, that is, two signal paths. One signal path is from an originating terminal to a ground station via a satellite, and the other signal path is from the ground station to a destination terminal via the satellite. In a mobile satellite system with a geosynchronous earth orbit satellite, if a connection is established between two mobile users through a gateway station, and two satellite hops are used, the delay from one user to the other user will be approximately 540 milliseconds (ms), which is generally unacceptable for voice communication.
A number of single-hop MSAT systems also exist; however, these systems are disadvantageous because they do not provide for a signaling channel between the originating and terminating terminals and a gateway station during a single-hop, terminal-to-terminal call. The MSAT system described in the aforementioned U.S. patent application of Chandra Joshi for xe2x80x9cA Mobile Satellite System and Method for Implementing A Single-Hop Terminal-to-Terminal Callxe2x80x9d, which is incorporated herein by reference, provides such a signaling channel between the originating terminal and the terminating terminal and a gateway station controller at the gateway station with which they are both registered. To establish a terminal-to-terminal call in this system, two traffic channels are used for each terminal. For each of the participating terminals in a terminal-to-terminal (ftT) call, a first pair of satellite channels are used by the terminals to set-up the TtT call. Once the direct satellite link has been established and the terminals have been assigned to the corresponding cross-connected satellite channels, the original pair of satellite channels are released.
In accordance with the present invention, an MSAT system is provided which optimizes satellite resources when implementing a single-hop TtT call. The MSAT system improves the voice quality of a terminal-to-terminal (Ttl) call by providing a connection with a single satellite hop, thereby reducing the aforementioned propagation delay to approximately 270 ms. The MSAT system requires only one pair of traffic channels, thereby optimizing the use of satellite resources and, at the same time, offering the same voice quality as an MSAT system which employs the use of two pairs of traffic channels for call set-up.
In accordance with an aspect of the present invention, satellite channels for the call path and a signaling channel during a single-hop TtT call are assigned to the participating terminals at an earlier stage during the call set-up procedure than in an MSAT system employing two pairs of satellite channels. Thus, only a single pair of satellite channels are assigned to the terminals for both call establishment and the call path during the TtT call, as opposed to two pairs of satellite channels.
In accordance with another aspect of the present invention, a test message for signaling channel (e.g., TTCH) validation is transmitted from the network (e.g., from a gateway station controller) to each of the terminals.
In accordance with yet another aspect of the present invention, the network issues the TTCH test message on a Radio Resource layer message for transmission to each terminal on its assigned satellite channel for signaling during the TtT call. The terminals repeat the message on the assigned satellite channels for call traffic (e.g., a traffic channel (CH)) to the network.
In accordance with another aspect of the present invention, the MSAT system performs another channel assignment procedure if a direct satellite communication link (e.g., an L-L link) cannot be successfully established between the participating terminals.